The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. All references discussed herein, including patent and non-patent literatures, are incorporated by reference into the current application.
Tube waves, otherwise known as Stoneley waves, are plane pressure waves that propagate through a tubular medium, or an annulus. In some cases, these waves reflect from changes in the characteristic impedance of the medium. Examples of such changes include: pipe diameter, closed end, free surface, gas bubble, compressibility, density, speed of sound, pipe elastic modulus, pipe supporting material (or lack thereof), holes with flow capacity, etc. With some knowledge of the wellbore geometry and/or the speed of the tube wave, the complex reflection patterns can be interpreted to yield useful information about the wellbore. Some examples of such information include locating the top of cement, identifying the setting of cement, locating which perforations in a well are passing fluid, confirming shifting of control valves, locating coiled tubing relative to downhole features, etc. One particular advantage of using methods based upon tube waves, is information about the bottom of the well can be gleaned using only surface equipment. A particular challenge in applying these techniques is developing a repeatable and reliable means to generate useful tube wave forms. Figures of merit for these sources include rate of pressure change, frequency spectrum, peak power, total energy, repeatability, and reliability.
U.S. Pat. No. 3,254,524 discloses a method and apparatus for testing tubular equipment such as a pipe. A mechanical shock wave is generated by suddenly obstructing a moving fluid, causing a local expansion of the fluid followed by a reversely directed pressure or shock wave that is propagated through the fluid, a phenomenon commonly referred to as “water hammer”. A centrifugal pump is employed to move the fluid in a closed circuit of pipes and to maintain the fluid under a constant pressure. A fast-acting valve is connected to the pipe line downstream from the test specimen. A sudden close of the valve generates a shock wave that propagates reversely through the test specimen and therefore measures the feature of the test specimen.
U.S. Pat. No. 3,979,724 discloses a method and apparatus for determining the position of the bottom end of a long pipe in a deep water-filled borehole. A shock wave is first generated in the water at the surface end of the pipe. The shock wave travels down the pipe to the bottom end of the pipe and passes into the liquid in the borehole, generating an expanding seismic wave in the earth. A plurality of geophones is set out at the surface of the earth to detect the arrival of the seismic wave, based on which the position of the end of the pipe is calculated. In some embodiments, a chamber filled with a combustible mixture is detonated by a spark plug to make the shock wave. In some other embodiments, a chamber containing one or more explosive materials is detonated to produce the shock wave. In some further embodiments, a high pressure liquid is provided through a pipe and a valve to a disc that is scaled across an opening connected to a chamber. The disc is frangible and at a selected pressure of liquid on its surface, will fracture and explosively permit the pressurized liquid in the pipe to expand into the chamber and initiate a shock wave therein.
U.S. Pat. No. 6,401,814 discloses a method for determining the location or displacement of a cementing plug during a cementing operation by transmitting one or more pressure pulses through the fluid in the wellbore. The pressure pluses are reflected off of the plug and received by a pressure sensor. Information regarding the timing of the reflected pressure pulses may be used to determine the location or displacement of the plug. A valve can be opened momentarily to vent pressure from a flowline and, thus, transmit a negative pressure pulse through the fluid in the casing string. Alternatively, an air gun can be used to transmit a positive pressure pulse through the fluid in the casing string. Alternatively, a pump can be operated in a manner to transmit a pressure pulse, such as by varying the pump's motor speed or by momentarily disengaging the motor from the pump, etc.
As disclosed in published U.S. Pat. App. No. 20080239872 A1, achieving accurate, real-time measurements during well completion and stimulation treatments has long been a goal in the oil and gas industry. Accurate measurement of bottom hole pressure during fracture treatments, for example, would allow an operator to observe fracture growth trends in real-time, and change treatment conditions accordingly. Similarly, location of balls seated in perforations would facilitate acid diversion treatments. However, real-time measurements of borehole completion and stimulation treatments are rarely performed with current technology because the borehole environment is hostile to wiring and tends to rapidly attenuate electromagnetic signals. For example, the abrasiveness of the fracturing slurry is destructive to any exposed cable placed in the wellbore for delivering data to the surface.
U.S. Pat. App. No. 20090159272 A1 discloses that tube waves may be used for detection and monitoring of feature state to enhance stimulation operations and remediate failure conditions. For example, proper sealing of perforations may be confirmed based on lack of a reflection of a tube wave by the perforations. Alternatively, at least one of amplitude, frequency, attenuation, dispersion and travel time associated with a tube wave and reflection may be used to determine feature state. If a sealant fails during treatment then the failure condition is indicated by appearance of a tube wave reflection. Consequently, the stimulation operation can be stopped in a timely manner, and remediation by means, for example, of pumping diversion fluid or dropping of balls, can be reinitiated until the difference between the expected responses and responses measured by the instrument along the segment to be stimulated confirm that sealing has taken place and that stimulation of the intended zone can resume. Further, specific remediation steps may be selected based on response of the borehole system to tube waves. The efficacy of the selected remediation steps may also be determined by response of the borehole system to tube waves during or after execution of those steps.
U.S. Pat. App. No. 20080236935 A1 discloses that tube waves may be used to transmit an indication of the depth at which a condition is detected in a well. In particular, the depth is calculated based on the difference in arrival time at the surface of a first tube wave which propagates directly upward in the borehole and a second tube wave which initially travels downward and is then reflected upward. The tube waves may be generated by a canister designed to implode at a certain pressure.
WO2009086279 discloses methods and systems for measuring acoustic signals in an annular region. The system includes a tool housed in a tool housing for deployment downhole in a borehole, and an acoustic transducer mounted on the tool. The acoustic signals can be measured by sensors mounted on a borehole wall or within the downhole tool.
However, there remains a need to further improve the system and method for generating tube waves for use in liquid filled boreholes penetrating subterranean formations.